[PATCH 05/17] nvme: wire-up support for async-passthru on char-device.

[Christoph Hellwig]

On Wed, Mar 16, 2022 at 04:50:53PM +0200, Sagi Grimberg wrote:
>>> I know, and that was my original question, no one cares that this
>>> interface completely lacks this capability? Maybe it is fine, but
>>> it is not a trivial assumption given that this is designed to be more
>>> than an interface to send admin/vs commands to the controller...
>>
>> Most people don't really care about or use multipath, so it's not a
>> primary goal.
>
> This statement is generally correct. However what application would be 
> interested in speaking raw nvme to a device and gaining performance that
> is even higher than the block layer (which is great to begin with)?

If passthrough is faster than the block I/O path we're doing someting
wrong.  At best it should be the same performance.

That being said multipathing is an integral part of the nvme driver
architecture, and the /dev/ngX devices.  If we want to support uring
async commands on /dev/ngX it will have to support multipath.